In the production of semiconductor devices and liquid crystal displays, rapid progress has recently been made in fining of a pattern with the progress of a lithography technology. As a technique for fining of the size, shortening of the wavelength of an exposure light source is generally performed. Specifically, while ultraviolet rays typified by g-ray and i-ray have hitherto been used, mass production of semiconductor devices using a KrF excimer laser or an ArF excimer laser has recently started. Also, a study about a F2 excimer laser having a shorter wavelength than that of these excimer lasers, electron beam, extreme ultraviolet rays, and X-rays have been made.
Also, as one of resist materials which satisfy high resolution capable of reproducing a pattern having a fine size, a chemically amplified resist composition containing a base resin wherein alkali solubility varies by an action of an acid, and an acid generator which generates an acid upon exposure is known. The chemically amplified resist composition includes, for example, a negative chemically amplified resist composition containing an alkali soluble resin, an acid generator, and a crosslinking agent, and a positive chemically amplified resist composition containing a resin wherein alkali solubility enhances by an action of an acid, and an acid generator.
At present, as a base resin of a resist in an ArF excimer laser lithography, a resin (acrylic resin) having a constituent unit derived from (meth)acrylic acid is mainly used because it is excellent in transparency to light of about 193 nm.
In these acrylic resins, a polycyclic alicyclic group such as adamantyl group, as a substituent of the ester moiety of a (meth)acrylate ester, is commonly introduced so as to improve etching resistance. For example, Japanese Unexamined Patent Application, First Publication No. 2003-167347 proposes a polymer comprising a constituent unit derived from a (meth)acrylate ester having an acid dissociable dissolution inhibiting group in the ester moiety, a constituent unit derived from a (meth)acrylate ester having a lactone skeleton such as γ-butyrolactone skeleton in the ester moiety, and a constituent unit derived from a (meth)acrylate ester having a polycyclic group including a polar group such as hydroxyl group in the ester moiety.
However, a resist using such a polymer has a problem such as poor affinity for an alkali developing solution. Poor affinity for an alkali developing solution can cause defects on the surface of a resist pattern after the development (development defects) and roughness on the surface of the side wall of a resist pattern (line edge roughness (LER)). The development defects mean entire inconveniences detected when the developed resist pattern is observed right above using a surface defect inspection equipment (trade name “KLA”) manufactured by KLA-TENCOR CORPORATION and these inconveniences include, for example, scum, foam, dust, bridge between resist patterns, irregular color, and precipitate after the development. Development defects and LER may exert an adverse influence on formation of a fine semiconductor device.
As a method of enhancing affinity for an alkali developing solution, for example, there can be employed a method of decreasing the proportion of a constituent unit having a highly hydrophobic acid dissociable dissolution inhibiting group in the above polymer or increasing the proportion of a constituent unit having a polar group. However, when these methods are used, resolution of the resulting resist pattern deteriorates.